1. Field of the Invention
The present invention relates to an electromagnetic flowmeter that measures the flow rate or the like of electro-conductive fluids, and in particular to an electromagnetic flowmeter that carries out empty pipe detection, that is, whether the inside of the pipe is filled with fluid or not, as well as detects the presence of insulating materials adhering to the detecting electrodes and measures the electrical conductivity (hereafter simply called xe2x80x9cconductivityxe2x80x9d) of the fluid to be measured.
2. Description of the Prior Art
As conventional electromagnetic flowmeters that carry out empty pipe detection, a configuration in which empty pipe detection is performed by a circuit which applies an alternating voltage having a frequency of 1/(an even number) of the excitation frequency, to the detecting electrodes inside the pipe, is disclosed in Japanese Patent No. 2880830. In addition, a configuration in which the above empty pipe detection is performed by a circuit that applies an alternating voltage having a frequency asynchronous with the excitation frequency is disclosed in Japanese National Publication of Patent Application No. 9-502267 (1997). Further, Japanese Patent Application Laid-Open No. 8-29223 (1996) discloses a configuration in which alternating signal generators that supply alternating currents are provided and the above empty pipe detection is performed by supplying to each detecting electrode in-phase alternating currents whose frequencies are sufficiently low.
In addition to the above, a conventional configuration to detect the extent of adhesion of insulating materials that adhere to detecting electrodes, is disclosed in Japanese Patent No. 3018310.This patent discloses a configuration such that, in an electromagnetic flowmeter which carries out empty pipe detection by comparing the detecting electrode potential of the detector with a reference voltage and comprises a constant current circuit that is provided with a current control means to change over and reverse the polarity of the current, the current is supplied to the detecting electrodes by changeover and inversion of the polarity upon detecting adhesion inside the pipe.
However, the configuration mentioned in Japanese Patent No. 2880830 is easily influenced by flow noise caused by the fact that fluid flows, due to the handling of signals whose frequency is smaller than the excitation frequency. In addition, since a large alternating voltage for empty pipe detection is generated in the flow signal even in the non-empty state due to the application of a low voltage, flow measurement is easily affected by the empty pipe detection circuit.
Further, in the configuration mentioned in Japanese National Publication of Patent Application No. 9-502267, since the result of flow sampling cannot avoid including the empty pipe detection signal, a number of averaging processes become necessary. For improving such influences, it is considered that the frequency of the empty pipe detection signal is made higher so that the flow signal and the empty pipe detection signal can be separated with a filter. However, in some cases, measured electrode impedances do not show accurate values due to structural dispersion in the electrode portions. Also, since a large alternating voltage for empty pipe detection is generated in the signal even in a not-empty state, flow measurement becomes to be easily affected by the empty pipe detection circuit.
Furthermore, in the configuration mentioned in an application of Japanese Patent Application Laid-Open No. 8-29223, since the empty pipe detection signal is always included in the result of flow sampling because the supplied alternating current signal is not synchronized with the excitation current, a number of averaging calculations become necessary. Also, the empty pipe detection signal is easily influenced by flow noise generated by the fact that fluid flows because a signal whose frequency is smaller than the excitation frequency is handled.
In the configuration mentioned in Japanese Patent No. 3018310, there is a problem that the means for empty pipe detection is easily influenced by the polarization voltage of the electrodes because direct current rather than alternating current is employed for detection.
In addition, the use of electromagnetic flowmeters in the field of agricultural waste water, as an application of electromagnetic flowmeters, has recently been considered. However, in some cases, earth and sand effluent is mixed in waste water but an electromagnetic flowmeter cannot be used for monitoring earth and sand effluent. In particular, irregular sedimentation of earth and sand in the lower reaches of rivers may occur and affect the environment in some cases, and thus if an electromagnetic flowmeter that can easily monitor earth and sand contained in waste water can be achieved, then environmental effects could be assessed by using such an electromagnetic flowmeter.
The present invention is devised in view of the above circumstances. The objective of the present invention is to provide an electromagnetic flowmeter that can accurately detect insulating materials stuck inside the pipe and discriminate between the type of fluid to be measured. Means for achieving this objective are as follows:
employing alternating signal to detect adhesion of insulating materials and conductivity of the fluid inside the pipe,
using a frequency that is an integer multiple of the fundamental excitation frequency as a signal frequency of a constant current supply, as well as synchronizing the excitation frequency with the frequency of adherents detection circuit signal,
selecting a frequency that is not affected by the structural dispersion of the electrodes,
accurately determining the electrode impedance by providing an electrode impedance measuring circuit and measuring the electrode impedance in the vicinity of the excitation frequency,
realizing an electrode impedance measuring circuit that is not easily affected by fluid noise, and
accurately measuring the electrode impedance for which the flow signal measuring circuit and the electrode impedance measuring circuit do not interfere with each other.
Embodiments for the present invention to achieve the above objective are described below.
(1) An electromagnetic flowmeter provided with a pipe through which the fluid to be measured is passed, which applies a magnetic field to the above-described fluid driving the excitation coils with an excitation circuit and thereby measures the flow rate of the fluid passing through the above-mentioned pipe, comprising:
a pair of detecting electrodes to detect a flow signal corresponding to the flow rate of the fluid passing through the above-mentioned pipe,
an earth electrode whose potential is the reference potential at the time of flow rate measurement,
diagnosing signal generators that give diagnosing signals between the above detecting electrodes and the earth electrode, and
a diagnosis circuit to detect resistance values between the above detecting electrodes and the earth electrode as diagnostic signals.
(2) An electromagnetic flowmeter mentioned in (1), wherein the above-described diagnosing signal generators are constant current supplies.
(3) An electromagnetic flowmeter mentioned in (1), wherein the above-described diagnosing signal generators are constant voltage supplies.
(4) An electromagnetic flowmeter mentioned in any of (1) to (3), wherein the above-described diagnosing signal generators use alternating signals whose frequency is an integer multiple of the excitation frequency used in the above excitation circuit.
(5) An electromagnetic flowmeter mentioned in (4), wherein the above-described diagnosis circuit synchronizes the above excitation frequency with the above diagnostic signal frequency.
(6) An electromagnetic flowmeter mentioned in either (4) or (5), wherein the above-described diagnosing signal generators select the frequency of the above-mentioned alternating signal to be generated in the range that the rotators of each dipole forming capacitances constructed with the above detecting electrodes and the above fluid interface can keep track of the signal.
(7) An electromagnetic flowmeter mentioned in any of (1) to (6), wherein the above-described diagnosing signal generators apply the above identical alternating signals to a pair of detecting electrodes as the above diagnosing signals.
(8) An electromagnetic flowmeter mentioned in any of (1) to (6), wherein the above-described electromagnetic flowmeter is small, in which, the distance between detecting electrodes is small, and the above diagnosing signal is applied alternately to each electrode.
(9) An electromagnetic flowmeter mentioned in any of (1) to (8), wherein the above-described diagnosis circuit makes the sampling time of flow signal be xe2x80x9c1/(an integer multiple of the above alternating signal frequency)xe2x80x9d when the above alternating signal frequency is an odd-number multiple of the above excitation frequency.
(10) An electromagnetic flowmeter mentioned in any of (1) to (9), wherein the above-described diagnosis circuit calculates the fluid conductivity using measured resistance values of the above detecting electrodes.
(11) An electromagnetic flowmeter mentioned in any of (1) to (9), wherein the above-described diagnosis circuit detects the status of insulating materials adhering to the above detecting electrodes using the above measured detecting electrode resistance values.
(12) An electromagnetic flowmeter mentioned in any of (1) to (11), wherein the above-described diagnosis circuit is provided with an analog output and a wireless communication output that transmit measured resistance and fluid conductivity values to an upper-level distributed control system or a personal computer.
(13) An electromagnetic flowmeter mentioned in any of (1) to (10), wherein each of the above-described constant current supplies possesses both an AC constant current circuit and a DC constant current circuit.
(14) An electromagnetic flowmeter mentioned in (13), wherein a signal based on the DC constant current supplies is used for empty pipe detection.
(15) An electromagnetic flowmeter mentioned in any of (1) to (9), wherein the above-described diagnosis circuit applies diagnosing signals between the above detecting electrodes and the above earth electrode when the above pipe is empty and detects deterioration of insulation at the above detecting electrodes using the diagnostic signal thereof.
(16) An electromagnetic flowmeter mentioned in (1), wherein the above-described diagnosing signal generators employ a frequency that is not an integer multiple of and higher than the above excitation frequency.
(17) An electromagnetic flowmeter mentioned in (16), wherein the above-described diagnosis circuit employs the time of xe2x80x9c1/(an integer multiple of the above alternating signal frequency)xe2x80x9d as the sampling time of flow signal.
(18) An electromagnetic flowmeter mentioned in (16) or (17), wherein the sampling timing for the flow signal and the above-described alternating signal frequency are derived from the same clock.
(19) An electromagnetic flowmeter mentioned in (16) or (17), wherein the sampling timing for the flow signal and the above-described alternating signal frequency are derived from separate clocks and the sampling time is calculated by counting the frequency of the above alternating signal and using the frequency thereof.
(20) An electromagnetic flowmeter mentioned in (16) or (19), wherein the above-described diagnosing signal generators generate frequencies in the range that the rotator of dipoles forming capacitances constructed by the above detecting electrodes and the interface of the fluid can keep track of the signal.
(21) An electromagnetic flowmeter mentioned in any of (16) to (20), wherein the above-described constant current supplies apply the above identical alternating signal to a pair of detecting electrodes as the above diagnosing signal.
(22) An electromagnetic flowmeter mentioned in (16) or (20), wherein the flowmeter is small, in which the distance between the above-described detecting electrodes is small, and is devised to pass a current to each electrode alternately.
(23) An electromagnetic flowmeter mentioned in any of (1) to (22), wherein the above-described diagnosis circuit sets the frequency of the above diagnosing signal to four times or more the above excitation frequency and the above diagnostic signal is sampled at the latter half of the excitation waveforms.
(24) An electromagnetic flowmeter mentioned in any of (1) to (23), wherein the above-described diagnosis circuit is provided with a adhesion diagnosis circuit that can alternately determine the fluid resistance values using at least two frequencies of the above alternating signal, discriminate the linear portion of the Cole-Cole plot based on the above resistance values, and select the frequency of the above diagnostic signal so that the above fluid resistance values by the diagnosing signal agree with the above resistance value at the above excitation frequency.
(25) An electromagnetic flowmeter mentioned in any of (1) to (15) or (24), using the dual-frequency excitation system that applies a magnetic field to the above-described fluid by driving the above excitation coils employing two excitation frequencies through the above excitation circuit, and provided with:
a means that synchronizes the excitation signal and the above flow signal with the above diagnosing signal,
a means that makes the frequency of the above diagnosing signal be an intermediate frequency between the high and low frequencies of the above two excitation frequencies, and
a means that sets the above diagnosing signal frequency as an even-number multiple of the above low frequency and also sets the above diagnosing signal frequency as 1/(an even number) of the above high frequency; further comprising an adhesion diagnosis circuit in which the low frequency differential noise components are removed at the latter half of the above low frequency period for the sampling of the above diagnostic signal and the sampling interval is composed of the time for one period of the above high frequency, in which the influence of high frequency noise components is removed, and the latter half of the excitation waveform.